Welcome Back The University of Jordan Summer 2017 By Dr. Darwish Badran and Dr. Shatarat Department of Anatomy and Histology School of medicine The University of Jordan Summer 2017

THE PITUITARY GLAND also known as the HYPOPHYSIS Master organ

The pituitary THE SELLA TURCICA It is a pea-sized Weighs 0.5 g in males and 1.5 g in multiparous women It is centrally located at the base of the brain, where it lies in a saddle-shaped depression of the sphenoid bone called THE SELLA TURCICA location A short stalk, the infundibulum connects the pituitary gland to the hypothalamus.

Radiology

THE SELLA TURCICA (hypophyseal fossa)

The pituitary

The pituitary gland is composed of two functional tissues Neural (secretory) tissue Posterior lobe (Neurohypophysis) Glandular epithelial tissue The Anterior lobe (Adenohypophysis)

Each endocrine gland has Embryological origins Embryology Important Each endocrine gland has two different Embryological origins

The two portions are of different embryologic origin The posterior lobe of the pituitaryis derived from a downgrowth (the future infundibulum) neuroectoderm of the floor of the third ventricle (the diencephalon) of the developing brain The anterior lobe of the pituitary gland is derived from an evagination of the ectoderm of the oropharynx toward the brain Rathke’s pouch

The anterior lobe of the pituitary gland consists of three derivatives of Rathke’s pouch: 1-Pars distalis which comprises the bulk of the anterior lobe of the pituitary gland and arises from the thickened anterior wall of the pouch

a thin remnant of the posterior wall of the pouch It is not part of the pituitary gland The median eminence  is part of the hypothalamus from which regulatory hormones are released 3-Pars tuberalis which develops from the thickened lateral walls of the pouch and forms a sheath around the infundibulum 2-Pars intermedia a thin remnant of the posterior wall of the pouch

The embryonic infundibulum gives rise to the posterior lobe of the pituitary gland Infundibulum, which is continuous with the median eminence and contains the neurosecretory axons forming the hypothalamohypophyseal tracts

The posterior lobe consists of the following: •Pars nervosa, which contains neurosecretory axons and their endings

Gross Anatomy

Superiorly A circular fold of dura mater, the diaphragma sellae forms the roof of this fossa Superiorly The diaphragma sellae is pierced by a small central aperture through which the pituitary stalk passes, and it separates the anterior part of the upper surface of the gland from The optic chiasma.

Laterally The hypophysis is bound on each side by the cavernous sinuses and the structures that they contain.

The cavernous sinuses and the structures that they contain.

Inferiorly The sphenoid air sinus it is separated from the floor of the fossa by a large, partially vacuolated venous sinus The sphenoid air sinus endoscopic transnasal applications in many pituitary surgical centers!!!!!

Blood supply segment of The internal carotid artery Cavernous sinus Hypophysial arteries are branches of the intercavernous segment of The internal carotid artery The inferior branch supplies the posterior lobe of the pituitary gland The superior branch leads into the median eminence to start the hypophysial portal system to the anterior lobe

The pars tuberalis Median eminence Infundibulum Blood supply A-Superior hypophyseal arteries These vessels arise from the internal carotid arteries and posterior communicating artery of the circle of Willis They supply The pars tuberalis Median eminence Infundibulum

Inferior hypophyseal artery B-Inferior hypophyseal arteries Divides into medial and lateral arteries Inferior hypophyseal artery Form an arterial ring around the infundibulum Supply the neurohypophysis

primarily supply the parsnervosa The inferior hypophysial vessels arise solely from the internal carotid arteries primarily supply the parsnervosa An important functional observation is that most of the anterior lobe of the pituitary gland has no direct arterial supply!!!!! Inferior hypophyseal arteries

Superior hypophyseal arteries hypophyseal portal veins The hypothalamohypophyseal portal system provides the crucial link between the hypothalamus and the pituitary gland. Superior hypophyseal arteries give rise to fenestrated capillaries (the primary capillary plexus). drain into hypophyseal portal veins They run along the pars tuberalis give rise to a second fenestrated sinusoidal capillary network (the secondary capillary plexus) This system of vessels carries the neuroendocrine secretions of hypothalamic nerves from their sites of release in the median eminence and infundibulum directly to the cells of the pars distalis

Venous drainage Most of the blood from the pituitary gland drains into the cavernous sinus and then into the systemic circulation. Some evidence suggests, however, that blood can flow via short portal veins from the pars distalis to the pars nervosa and that blood from the pars nervosa may flow toward the hypothalamus. These short pathways provide a route by which the hormones of the anterior lobe of the pituitary gland could provide feed back directly to the brain without making the full circuit of the systemic circulation.

The posterior pituitary Neurohypophysis is neural tissue and is formed by the distal axons of The supraoptic nucleus (SON) and The paraventricular nucleus (PVN) of the hypothalamus.

The blood supply for the posterior pituitary is from The axon terminals store neurosecretory granules that contain vasopressin The blood supply for the posterior pituitary is from the inferior hypophysial arteries, The venous drainage is into the cavernous sinus and internal jugular vein

the “posterior pituitary bright spot.” The stored vasopressin in neurosecretory granules in the posterior pituitary produces a bright signal on (MRI) the “posterior pituitary bright spot.” The posterior pituitary bright spot is present in most healthy individuals and is absent in individuals with central diabetes insipidus.

Clinical applications

(SHEEHAN SYNDROME

which are drained by the hypophysial portal vessels,. The pituitary gland enlarges during pregnancy (primarily because of lactotroph hyperplasia) portal venous blood supply is uniquely vulnerable to changes in arterial blood pressure severe postpartum uterine hemorrhage, spasm of the infundibular arteries, which are drained by the hypophysial portal vessels,. could result in pituitary infarction. If the lack of blood flow continued for several hours, most of the tissues of the anterior pituitary gland infarcted; when blood finally started to flow, stasis and thrombosis occurred in the stalk and the adenohypophysis

The optic chiasm lies above the diaphragma sellae. Pituitary Adenoma The optic chiasm lies above the diaphragma sellae. The most common sign that a pituitary tumor has extended beyond the confines of the sella turcica is a visual defect caused by the growth pressing on the optic chiasm.. The most frequent disturbance is a Bitemporal hemianopsia which is produced by the tumor pressing on the crossing central fibers of the chiasm and sparing the uncrossed lateral fibers.

Craniopharyngioma is the most common tumor found in the region of the pituitary gland in children and adolescents and constitutes about 3% of all intracranial tumors and up to 10% of all childhood brain tumors. Craniopharyngiomas histologically benign epithelioid tumors arising from embryonic squamous remnants of Rathke pouch—may be large (e.g., > 6 cm in diameter) and invade the third ventricle and associated brain structures.

Histology

water, carbohydrate lipid, gas The HEMATOXYLIN stains nucleic acids (plus calcium deposits and bacteria) blue. The EOSIN stains most proteins (actually, arginine and lysine) pink. Clear areas represent water, carbohydrate lipid, gas

Nuclei will always stain Blue with the Hematoxylin. 

The cytoplasm of cells will stain according to its composition.

The anterior pituitary also contains one type of chromophobe  Two types of chromophils (cells which take up stain) called acidophils and basophils. The anterior pituitary also contains one type of chromophobe  (cells which stain only weakly) 

Histologists identified three types of cells according to their staining reaction, namely Basophils (10%) Acidophils (40%) Chromophobes (50%)

Adenohypophysis – high power The adenohypophysis contains 3 cell types: -acidophils (stain red) -basophils (stain blue) -chromophobes (pale stain) The adenohyphysis stains red-blue on low power because of the acidophils and basophils

Importance of different colors? Acidophils secrete growth hormone and prolactin Basophils secrete TSH, LH and FSH and ACTH Chromophobes are undifferentiated cells

Cells of the adenohypophysis Chromophils Acidophils Basophils Chromophobes

Cells of the Adenohypophysis 1- Chromophobes small weakly stained cells represent stem cells or (most likely) partially degranulated chromophils * Folliculostellate cells: large cells with many processes of unknown function

Chromophils Acidophils Somatotops Mammotrops Basophils Gonadotrops Thyrotrops Corticotrops

1- Somatotrops: Form ~ 50% of the total number of chromophils. Occur in clumps and clusters Central nucleus Rod shaped mitochondria Many rER Many secretory granules (secrete GH) Moderate Golgi Action of GH: acts on growth of long bones via insulin-like growth factors synthesized in the liver.

2- Mammotrops Form 15-20% of chromophils Occur singly Small polygonal cells Organelles are ill-defined During lactation organelles increase in size and number Secrete prolactin Action of prolactin: promotes milk secretion.

3- Gonadotrophs Form ~ 10% of chromophils. Rounded cells. Prominent nucleus. Many granules with variable size. Cytoplasm contains well developed Golgi, many rER. Secrete FSH and LH. Action of FSH: promotes ovarian follicle development and estrogen secretion in women, and spermatogenesis in men. Action of LH: promotes follicular maturation and progesterone secretion in women and Leydig secretion in men.

4- Thyrotrops Form ~ 5% of chromophils. Located away from sinusoids. Cytoplasm contains many small organelles. Secrete TSH. Action of TSH: stimulates thyroid hormone synthesis, storage, and liberation.

5- Corticotrops Form 15-20% of chromophils. Round-ovoid cells scattered through pars distalis. Eccentric nucleus with few organelles. Secrete ACTH. Action of ACTH: stimulates secretion of adrenal cortex hormones and regulated lipid metabolism.

Does not contain secretory cells. Contains axons of secretory nerves; their mother cells are present in the paraventricular and supraoptic hypothalamic nuclei. Pituicytes are the most numerus cells. Pituicytes resemble astrocytes.

Axons of neurons transport ADH and oxytocin into the pars nervosa. Secretory neurons have larger diameter but are histologically and functionally similar to other neurons. Axons of neurons transport ADH and oxytocin into the pars nervosa. Secretory products accumulate in the distal part of the axon in Hering bodies. Hering bodies appear slightly acidophilic. Secretory products are surrounded by a membrane and bound to neurophysin. Nerve impulses trigger the release release of peptides from neurosecretory bodies.

Most Oxytocin is released from paraventricular nuclei. Most ADH is released from supraoptic nuclei.

ADH facilitates resorption of water from the distal tubules and collecting ducts of the kidney by altering the permeability of the cells to water.

Oxytocin promotes contraction of smooth muscles of the uterus and myoepithelial cells of the breast.